Because bulimic pathology is prevalent in adolescent girls, shows a chronic course, results in serious health problems, and is resistant to treatment, it is vital to develop prevention programs for this disorder. We plan to conduct an effectiveness trial of a targeted eating disorder prevention program that produced intervention effects for bulimic pathology, risk factors for bulimic pathology, and risk for future onset of obesity that persisted up to two years and outperformed alternative interventions in controlled efficacy trials conducted by our lab and independent labs. This proposal is the product of a 12-year program of research that identified risk factors for bulimic pathology and conducted efficacy trials of preventive interventions based on this generative research. In this dissonance-based program, an example of translational research, at-risk girls with body image concerns who have internalized the culturally sanctioned thin-ideal voluntarily engage in verbal, written, and behavioral exercises in which they critique this ideal. These counter-attitudinal activities putatively result in decreased internalization of the thin-ideal and consequent reductions in body dissatisfaction, negative affect, dieting, and bulimic pathology. We plan to test whether this targeted program produces intervention effects when delivered by natural providers in real world settings under ecologically valid conditions. We will randomly assign 330 at-risk girls (aged 14- 18) recruited from two entire school districts to the dissonance program or a psycho educational control condition and follow them for two years. School counselors will recruit and screen participants and deliver both interventions in high schools. We will test whether (1) the dissonance program results in greater decreases in bulimic pathology and risk factors for bulimic pathology than the control program, (2) intervention effects are mediated by change in thin-ideal internalization, (3) certain factors moderate program effects (e.g., poor insight regarding the costs of pursuing the thin-ideal), and (4) intervention effects occur for other ecologically meaningful outcomes (e.g., risk for obesity onset and psychosocial functioning). The proposed trial should advance the field because it will be the first effectiveness trial of an eating disorder prevention program and it will be more methodologically rigorous than past trials (e.g. will use random assignment, an attention control condition, blinded diagnostic interviews, multiple-reporter data, and a long-term follow-up).